NO. 5 PRE-DEVONIAN PALEOZOIC FORMATIONS 349 



The massiveness of Robson is best illustrated by plate 95, which 

 is a view from the northwest. It gives the profile of the tnountain 

 from Lake Kinney to the summit, in which the massive beds of lime- 

 stone form cliff above cliff, separated by the talus slope where the 

 softer, more easily broken down, thin-bedded limestones have given 

 way. On the left a section of the mountain has been broken down, 

 the strata sloping to the northeast, forming what is known as the 

 Helmet. This is illustrated in detail by plates 96 and 98. 



This displacement appears to have been caused by faulting on 

 both the northeastern and southwestern side of the mass forming the 

 Helmet. The northeastern fault appears also to have affected the 

 position of the strata of lyatunga Mountain in relation to Robson (see 

 fig. 34). The strata on the summit of lyatunga belong to the Lower 

 Chushina formation, which is of the same age as the beds of Billings 

 Butte on the opposite side of the great glacier. 



My present impression is that the northeastern side of the Robson 

 synclinorium broke, leaving a great block of unsupported strata 

 that dropped down and tilted to the northeast. This break presum- 

 ably shattered the strata to the southeast of the Helmet, and thus aided 

 materially the erosion of the great cirque between lyatunga and 

 Mount Resplendent. 



The geologic section exposed on the right (west) side of the peak 

 above Lake Kinney is formed of Middle Cambrian limestones to the 

 first long talus slope (pi. 95). From here up for about 3,000 feet 

 (914.4 m.), the limestones are of Upper Cambrian age to the top of 

 the low dark cliff at the foot of the talus slope of the higher portion 

 of the cliffs. Above this, as far as known, the limestones are probably 

 of Upper Cambrian and Lower Ozarkian age. This section is out- 

 lined by the diagrammatic drawing, figure 33. 



The great cirque on the eastern slope of Robson is beautifully 

 illustrated by plate 96, where the immense masses of snow accumulate 

 on the upper slopes of Robson Peak and its southeastern ridge, 

 joining it with Mount Resplendent (11,173 feet, 3.405.5 m.). The 

 southwestern face of Robson is illustrated by plate 97, in which the 

 regularity of the bedding of the limestone is beautifully shown ; also, 

 the steepness of the upper slopes of this side of the mountain. The 

 appearance of the sandstones and quartzites that rise from beneath 

 the peak on the southwest is shown by plate 97. It was not possible 

 to obtain a photograph of similar sandstones and quartzites which 

 rise from beneath the mountain upon the southern side and form high 

 rounded hills north and south of Rainbow Brook. 



